GAZA — Palestinian militants fired an antitank missile on Saturday at an Israeli military jeep patrolling Israel’s border with Gaza, and five Palestinians, including four civilians, were killed when Israel returned fire with tank or artillery shells, officials said.

The Israeli military said four of its soldiers were wounded, one seriously, in the antitank missile attack. The Gaza Health Ministry said about 26 Palestinians were wounded by Israeli fire.

Gaza militants then fired a barrage of rockets and mortar shells into southern Israel; one of the militants was killed by a return airstrike.

The deadly surge of violence reflected the growing volatility along the border between Israel and Gaza, the Palestinian coastal enclave that is controlled by the militant Islamic group Hamas. An atmosphere of confrontation has been simmering for months, and has peaked in several rounds of clashes between militant groups firing rockets from Gaza into southern Israel and Israeli forces carrying out airstrikes against the militant groups.

The leftist Popular Front for the Liberation of Palestine claimed responsibility for Saturday’s attack on the military jeep. Soon after the antitank missile was fired, Israeli forces aimed shells at a hill on the Gaza side of the border where a group of militants was monitoring the Israeli forces, according to a Palestinian witness, Mohanned Abu Alatta, 20, who was wounded.

Mr. Abu Alatta, interviewed at Al Shifa hospital in Gaza, said civilians who were gathered in a mourning tent nearby, including several teenage boys, ran to the scene to help the wounded militants and were themselves hit by subsequent shells. The four civilians killed were identified as Ahmed Mustafa Harara and his cousin Muhammad Osama Harara, who were both 17; Mattar Abu Alatta, 19, a distant relative of Mr. Abu Alatta; and Ahmed Kamil Dardasawi, 20.

The Gaza Health Ministry reported that at around the same time, Israeli machine-gun fire wounded six Palestinians, two of them children, in a residential neighborhood east of Khan Younis, further south along the border. A Palestinian boy was fatally shot on Thursday during clashes between Israeli forces and militants in the same area.

In recent years, Hamas has largely adhered to an informal cease-fire with Israel, but in recent months it has joined more radical groups, including Islamic Jihad and several militants inspired by Al Qaeda, in attacking Israel and avenging the deaths of its militants in Israeli raids.